Planographic printing plates



3,131,630 PLANOGRAPHIC PRINTING PLATES Alexander Spencer, Kingsbury, London, England, assignor to Gestetner Limited, London, England, a British company No Drawing. Filed June 3, 1960, Ser. No. 33,629 Claims prioriltz', application Great Britain June 8, 1959 Claims. (Cl. 101149.2)

This invention relates to planographic printing plates.

In recent years there have been developed various forms of so-called planographic printing plates which are effectively lithographic plates in which the image and nonimage areas of the plate are distinguished in that the former is oleophilic and therefore receptive to greasy printing ink and the latter is hydrophilic and therefore rejects such ink. These'plates are imaged either directly, for example by applying a greasy ink receptive image to the surface of the plate or may be pre-sensitized and the image produced by photographic or related means.

Basically therefore the plates must have a surface layer which can readily be rendered differentiallyink-receptive and ink-repellent. The base material of the plates may be metal, e.g. thin aluminium sheet, but probably the bulk of the plates manufactured are on wet-strength paper base. Many proposals have been made for the precise structure of the plates, including the provision of waterproofing layers for the paper, anti-curl coatings and the like.

The surface coating, which is to accept the image, is referred to as the planographic coating or layer and normally consists of a colloid film-forming material. This must be essentially hydrophilic but must be insolubilised. Suitable colloids which have been proposed are carboxymethylcellulose, polyvinyl alcohol and polyacrylic resins.

It has been proposed to render such colloid layers insoluble by the application of salts of multivalent metals, e.g. copper and zinc, applied as a wash to the surface of the coated plate. This however involves a separate insolubilisation step and it is more convenient to include in the planographic coating a material which, when the coating is dried, will automatically insolubilise it. Proposals of this type which have been made in the past however have presented considerable difiiculty since it is necessary that the insolubilising agent should not become effective before the coating is applied to the base sheet (or the coating solution becomes unusable) and that it should work rapidly and completely when the coating is dried (or else insolubilisation continues for a long period after thecoating is made so that the degree of insolubilisation is difficult to fix and there are economic difficulties).

It is an object of the present invention to provide a new method for preparing a self-insolubilising colloid tains 'a hardening agent for the hydrophilic colloid since in this way planographic printing plates may be obtained WhlCh will iaiford a larger number of copies before becoming unduly wcm.

It is found that if there is added to a solution of an I acid-soluble hydrophilic colloid, both a salt of a multivalent metal and a volatile acid, there is formed a soluble complex between the three which is quite stable at pH values below 7 but which when dried out decomposes rapidly to form an insoluble salt of the metal with the said colloid thus freeing the volatile acid which evaporates from the layer. The layer thus automatically insolubilises in sit-u. The composition advantageously also contains a hardening agent forthe-hydrophilic colloid in order that the layer should be given sutficient rigidity as a planographic printing layer that long runs of prints may be made from it, and the filler is included to give body to the layer and generallyto-render it more suitable for the acceptance ofan image.

The support sheet may be of any suitable material such as metal, e.g. foil of [aluminium or aluminium alloy, or paper, which may or maynot have received a treatment to improve its wet-strength, or plastic foil. The support may carry sub-coated layers (i.e. layers between the support sheet and the planographic layer) e.g. waterproofing layers or layers serving to improve the anchorage of the planographic layer to the assembly.

Any acid-soluble hydrophilic colloid which contains free hydroxy and/or carboxyl groups may be used (such groups being necessary in order that the colloid should form salts with multivalent metals) and particularly satisfactory results have been obtained by the use of cellulose derivatives such as carboxymethyl cellulose, vinyl compounds such as vinyl acetates containing a proportion of free hydroxyl groups, and acrylic compounds such as polymeric acrylates and substituted acrylates.

The salt of a multivalent metal which is employed is in no way critical and any such soluble salt is suitable. Examples are the sulphates, nitrates, chlorides, acetates, formates and other soluble salts of copper, iron, nickel, cobalt and aluminium.

The selection of the acid is critical in the sense that I it is essential that it should be volatile under the drying planographic coating for a planographic printing plate which avoidsthe difiiculties referred to.

According to the present invention there is provided a process for the-production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid containing free hydroxy and/ or carboxyl groups, one or more soluble multivalent metal salts and one or more volatile acids, and (b) a filler, thepH of the coating composition being below 7. ireferably, the composition further conconditions applied to the coated plate. Gencrally this means that the acid should have a boiling point below about C. Typical such acids are hydrochloric acid and the lower fatty acids, e.g. formic, acetic, propionic and butyric acids and the volatile substitution derivatives of such acids which still contain free carboxyl groups.

As already indicated it is advantageous to include in the planographic layer an agent which will have a hardening eifect on the colloid which is formed by decomposition of the complex. The particular hardening agent of choice will depend on the colloid used and other factors but generally the most satisfactory results are obtained by using a chromate or bichromate as the hardening agent, e.g. alkali metal, ammonium, calcium or copper chromates or bichromates.

Any filler known for use in the at of planographic layers may be employed in the present invention. Generally a white pigment material is preferred, e.g. china clay, blanc fixe, zinc oxide, titanium dioxide or talc, but any other white pigment or a coloured pigment may be employed. Of the commercially available fillers, china clay has been found to be most generally useful.

Due to the presence of the free volatile acid the coating composition has a pH value below 7 and generally it is preferred that it should be so formulated that it has a pH value below 5.

The coating compositions as aforesaid are conveniently applied by air-knife coating or brush coating, the coating weight being selected to suit the particular product being manufactured and genenally being within the range of 2 to 10 lbs. per ream (calculated as dried-down coating). The ream referred to is a ream of 500 sheet 20 inches x 30 inches.

The following examples in which all the parts are by weight will serve to illustrate the invention:

EXAMPLE I A. Preparation of a Paper-Base Support Wet strength paper (45 lb. per ream) is given a back coating to ensure that the final product does not curl. A typical formulation is as follows:

Parts Casein 15 Water 75 Warm, then add Ammonia 2 Parts China clay Water 70 When the clay has been thoroughly dispersed, the dispersion is mixed with the casein solution and then the following made up solution is added.

Parts Zinc chloride solution 198 Tw 2 Water 5 Ammonia 5 This casein-china clay slurry is coated on the wire side of the wet strength paper in a coating weight of 2-8 lbs./

ream.

The felt side of the wet strength paper is coated with This slurry is coated on to the felt side of the backcoated wet strength paper in a coating weight of 2-6 lbs./ ream. The so-prepared base paper is ready for the planegraphic coating.

B. Application of the Planographic Coating The following solutions were prepared:

Carboxy methyl cellulose solution: Parts Low viscosity sodium carboxy methyl cellulose 25 Water (warm) 400 Glacial acetic acid 80 B Clay slurry: Parts China clay 100 Water 150 Salt Solution No. l: Parts Copper sulphate 14 Water 50 When dissolved add:

Glacial acetic acid 4 Salt Solution No. 2: Parts Ammonium bichromate 8 Water 20 Glacial acetic acid 2 Salt Solution No. 3: Parts Ferric chlor 3 Water 20 Glacial acetic acid 10 A composite coating slurry was prepared from the above by mixing the clay slurry B with the carboxymethyl cellulose solution A and then simultaneously adding the Salt Solutions 1, 2 and 3. This slurry was coated on the undercoating of paper prepared as described above in coating weights between 2 to 10 lbs./ ream.

Compositions A and B were mixed and the salt solutions 1 and 2 added simultaneously. The resulting slurry was coated on the paper base described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE III The following formulations were prepared:

Parts Low viscosity carboxy methyl cellulose sodium salt- 25 Water 400 Glacial acetic a Parts China clay Zinc oxide 10 Water Salt Solution No. 1: Parts Zinc chloride 14.0 Water 80.0 Glacial acetic aci 12.0 Salt Solution No. 2: Parts Ammonium bichromate 6 Water 30 Glacial acetic acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to lbs. per ream.

Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE V The following formulations were prepared:

' Parts Low viscosity sodium carboxy methyl cellulose 25 Water... 400 Glacial acetic acid 80 Parts China clay 90 Titanium dioxide 10 Water 150 Salt Solution No. 1: Parts Copper sulphate 14.0 Water 80.0 Glacial acetic acid 12.0

Salt Solution No. 2: Parts Ammonium bichromate 6 Water Glacial acetic acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2- to 10 lbs. per ream.

EXAMPLE VI Glacial acetic acid 5 The following formulations were prepared: Formulations A and B were mixed and the salt solu- A 65 tions then added simultaneously. The resulting slurry Parts was coated on paper base prepared as described in Exam- 1 IA t Low viscosity sodium carboxy methyl cellulose 25 p e a a coming weight of 2 to 10 lbs per ream water 400 EXAMPLE IX Glacial acetic acid 80 70 The following formulations were prepared:

Parts Parts China clay- 90 Low viscosity sodium carboxy methyl cellulose 25 Zinc oxide 10 Water 400 Water 150 75 Formic acid 80 Salt Solution No. 1: Parts Nickel nitrate 14.0 Water 80.0

' Glacial acetic aci 12.0

Salt Solution No. 2:' Parts Ammonium bichromate"; 6 Water 30 Glacial acetic acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE VII The following formulations were prepared:

Parts Low viscosity sodium carboxy methyl cellulose---" 25 Water 400 Glacial acetic acid 80 Parts China clay Zinc oxide- 1 10 Water Salt Solution No. 1: Parts Cobalt chloride 14.0 Water 80.0 Glacial acetic acid 12.0

Salt Solution No. 2: Parts Ammonium bichromate 6 Water 30 ,Glacial acetic acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE VIII The following formulations were prepared:

Parts Low viscosity sodium carboxy methyl cellulose-. 25 Water 400 Glacial acetic acid 80 Parts China clay 90 Zinc oxide 10 Water 150 Salt Solution No. l: 1 Parts Aluminium sulphate 14.0 Water 80.0 Glacial acetic acid 12.0 Salt Solution No. 2 Parts Ammonium bichromate 6 Water 30 Parts China clay 90 Zinc oxide 10 Water 150 Salt Solution No. 1: Parts Copper sulphate 14.0 Water 80.0 Formic acid 12.0

Salt Solution No. 2: Parts Ammonium bichromate 6 Water 30 Formic acid 5 Salt Solution No. 3: Parts Ferric chloride 3.2 Water 20.0 Formic acid 10.0

Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to lbs. per ream.

EXAMPLE X The following formulations were prepared:

Parts Low viscosity sodium carboxy methyl cellulose 25 Water 400 Butyric acid 80 Parts China clay 90 Zinc oxide 10 Water 150 Salt Solution No. 1: Parts Copper sulphate 14.0 Water 80.0 Butyn'c arid 12.0

Salt Solution No. 2: Parts Ammonium bichromate 6 Water 30 Butyric acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Exam- Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE XII The following formulations were prepared:

u Parts Low viscosity sodium carboxy methyl cellulose 25 Water 400 Acetic acid Parts China clay Zinc oxide 10 Water Salt Solution No. 1: parts Copper chromate 14.0 Water 250 Acetic acid 250 Salt Solution No. 2: Parts Ammonium bichromate 6 Water 30 Acetic acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE XIII The following formulations were prepared:

Parts Sodium polyacrylate 25 Water 400 Acetic acid 80 Parts China clay 90 Zinc oxide 10 Water 150 Salt Solution No. 1: Parts Nickel nitr 14.0 Water 80.0 Acetic acid 12.0

Salt Solution No. 2: Parts Ammonium bichromate 6 Water 30 Acetic acid 5 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE XIV The following formulations were prepared:

Parts Low viscosity sodium carboxymethyl cellulose 25 Water 400 Glacial Acetic A 80 Parts China clay-.. 90 Zinc oxide 10 Water 150 Salt Solution No. 1: Parts Nickel nitr 14.0 Water 80.0 Acetic acid 12.0

Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to lbs. per ream.

EXAMPLE XV The following formulations were prepared:

' Parts Low viscosity sodium carboxy methyl cellulose 25 Water 400 Glacial acetic acid 80 Parts China clay 90 Zinc Oxide 10 Water 150 Salt Solution No. 1: Parts Zinc chloride 8.0 Water 40.0 Acetio 8.0

' Salt Solution No. 2: Parts Nickel sulphate 8.0 Water 40.0 Actic acid 8.0

Salt Solution No. 3: v Parts Copper chromate 8 Water 160 Acetic acid 160 Formulations A and B were mixed and the salt solu-' tions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

EXAMPLE XVI The following formulations were prepared:

' Parts Low viscosity sodium carboxy methyl cellulose Water a 400 Formulations A and B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA at a coating weight of 2 to 10 lbs. per ream.

1'0 EXAMPLE XVII The following formulations were prepared:

Formulations A and'B were mixed and the salt solutions then added simultaneously. The resulting slurry was coated on paper base prepared as described in Example IA in a coating weight of 2 to 10 lbs. per ream. Since the composition in this case contains no hardening agent for the hydrophilic colloid, the resulting plate effects a lesser number of satisfactory prints before becoming too damaged.

Whilst in all the foregoing examples the coating composition is directed to be applied to a paper base prepared as in Example IA it is to be understood that the coatings may be applied to paper base without an intervening undercoatingf The undercoating is generally preferred however as it tends to smooth out roughnesses in the support sheet and it may also serve to increase the anchorage of the layers of the product. It is further to. be understood that the coating weights of the planographic layer and the underlayers present may be varied as required.

To facilitate the production of fiat, non-curling sheets, the various coatings may be submitted to calendering after application.

It has been found that by means of the present invention planographic plates may be produced in which the planographic coating becomes insolubilised and reaches a state of equilibrium in a short period, e.g. only a few days, and that the resulting plates are capable of yielding greater numbers of copies than plates similarly prepared but in which other methods of insolubilisation have been employed.

I claim:

1. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, at least one multivilent metal salt and at least one volatile lower fatty acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

2. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a soluble salt of carboxymethyl cellulose, at least one multivalent metal salt and at least one volatile lower fatty acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

3. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a polyvinyl alcohol, at least one multivalent metal salt and at least one volatile lower fatty acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

4. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a soluble polyacrylate salt, at least one multivalent metal salt and at least one volatile lower fatty acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

5. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, at least one multivalent metal salt selected from the class consisting of soluble sulphates, nitrates, chlorides, acetates and formates of copper, iron, nickel, cobalt and aluminium and at least one volatile lower fatty acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

6. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a soluble salt of carboxymethyl cellulose, at least one multivalent metal salt selected from the class consisting of soluble sulphates, nitrates, chlorides, acetates and formates of copper, iron, nickel, cobalt and aluminium and at least one volatile lower fatty acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

7. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, at least one multivalent metal salt and acetic acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

8. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, at least one multivalent metal salt and formic acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

9. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, which is a soluble salt of carboxymethyl cellulose, at least one multivalent metal salt selected from the class consisting of soluble sulphates, nitrates, chlorides, acetates and formates of copper, iron, nickel, cobalt and aluminium, and acetic acid, (b) a filler, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

10. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, at least one multivalent metal salt and at least one volatile acid, (b) a filler, and (c) a chromate hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

11. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a soluble salt of carboxymethyl cellulose, at least one multivalent metal salt and at least one volatile acid, (b) a filler, and (c) a chromate hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

12. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a soluble salt of carboxymethyl cellulose, at least one multivalent metal salt selected from the class consisting of soluble sulphates, nitrates, chlorides, acetates and formates of copper, iron, nickel, cobalt and aluminum and acetic acid, (b) a filler, and (c) a chromate hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

13. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid, at least one multivalent metal salt and at least one volatile acid, (b), a filler containing china clay, and (c) a hardening agent for the hydrophilic colloid, the pH of the composition, being below 7.

14. A process for the production of a planographic printing plate which comprises applying to a support sheet a layer of a coating composition comprising (a) a soluble complex formed of an acid-soluble hydrophilic colloid which is a soluble salt of carboxymethyl cellulose, at least one multivalent metal salt selected from the class consisting of soluble sulphates, nitrates, chlorides, acetates and formates of copper, iron, nickel, cobalt and aluminum and acetic acid, (b) a filler containing china clay, and (c) a chromate hardening agent for the hydrophilic colloid, the pH of the composition being below 7.

References Cited in the file of this patent UNITED STATES PATENTS 2,230,981 Toland et a1. Feb. 4, 1941 2,534,650 Worthen Dec. 19, 1950 2,542,784 Van Dusen Feb. 20, 1951 2,550,326 Brown Apr. 24, 1951 2,635,537 Worthen Apr. 21, 1953 2,693,145 Mullen Nov. 2, 1954 2,724,665 Oransky et al Nov. 22, 1955 2,808,778 Newman et al Oct. 8, 1957 OTHER REFERENCES Hercules Sodium Carboxymethylcellulose, Pub. 1944. 

10. A PROCESS FOR THE PRODUCTION OF A PLANOGRAPHIC PRINTING PLATE WHICH COMPRISES APPLYING TO A SUPPORT SHEET A LAYER OF A COATING COMPOSITION COMPRISING (A) A SOLUBLE COMPLEX FORMED OF AN ACID-SOLUBLE HYDROPHILIC COLLOID, AT LEAST ONE MULTIVALENT METAL SALT AND AT LEAST ONE VOLATILE ACID, (B) A FILLER, AND (C) A CHROMATE HARDENING AGENT FOR THE HYDROPHILIC COLLOID, THE PH OF THE COMPOSITION BEING BELOW
 7. 